Solid-state microsecond capacitance charger for high voltage and pulsed power

ABSTRACT

A solid-state high-voltage pulse generator based on a three-phase chopper capacitance charger is described. In a first phase, an intermediate capacitor is resonance-charged via a diode. In a second phase, the intermediate capacitor is discharged to the load through one or more solid-state switches. In a third phase, the energy remaining in the intermediate capacitor is returned to a power-supply filter capacitor. In one embodiment, the three-phase chopper includes an intermediate capacitor that is charged by first and fourth branches of a bridge and discharged by second and third branches of a bridge. In one embodiment, each branch of the bridge includes a diode in series with an inductor. In one embodiment, a composite solid-state switch connects the intermediate capacitor to a primary winding of an output transformer such that the intermediate capacitor discharges through the primary winding. In one embodiment, a secondary winding of the output transformer is provided to an output load. In one embodiment, the output load is a reactive load. In one embodiment, the output load is a capacitive load.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.10/351,644, filed Jan. 24, 2003, titled “SOLID-STATE MICROSECONDCAPACITANCE CHARGER FOR HIGH VOLTAGE AND PULSED POWER,” which claimspriority benefit of U.S. Provisional Application No. 60/355,537, filedFeb. 6, 2002, titled “SOLID-STATE MICROSECOND CAPACITANCE CHARGER FORHIGH VOLTAGE AND PULSED POWER,” the contents of which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of solid-state high-voltage pulsepower generators.

2. Description of the Related Art

High voltage pulse generators with fast rise time are typically used todrive gas discharge loads such as lasers, devices for pollution controlapplications and for plasma chemistry. In the past, such pulsegenerators used thyratrons to generate the desired pulses. However,thyratrons are relatively unreliable and they have high complexityresulting in a high price. Solid state devices such as thyristors,MOSFET transistors and Insulated Gate Bipolar Transistors (IGBTs),although much lighter and more reliable than thyratrons, handle lesspower than a thyratron. In order to replace one thyratron, one needshundreds or thousands of solid state devices.

The power that each solid state transistor can produce is restricted byits saturation current (˜70 A) and by its breakdown voltage (˜600 V),giving a maximum pulsed power Pav=Isat×Ubd/2=21 KW. For most plasmaapplications, the desired pulse length is about 100 nanoseconds. Thismeans that the pulse energy the transistor can produce is typically nothigher than 2.1 mJ. If the repetition rate is increased to 50-100 kHz,then the power will have a reasonable value (100 w-200 w). The mainadvantage of short pulses (<100 ns) in plasma devices is the highelectrical strength of the gap that permits achievement of twice ortriple the mean temperature of electrons. If the repetition rate isincreased to more than 1000 Hz, the residual ionization will reduce theelectrical strength of the plasma gap and eliminate the advantage ofshort pulses. This problem is typically solved by increasing the pulselength of the solid-state pulse generator and using one more outputstages to compress the power. The second stage compressor, if desired,can be a spark gap, blumline, etc. To simplify the design of thecompressor, the pulse length of the charger is typically held to a fewmicroseconds or even as short as 1-2 microseconds.

Even when using an output compressor, in order to replace one thyratronone needs hundreds or thousands of solid state devices. The cost of allthese devices is comparable to the cost of one thyratron, but thereliability of solid state devices is higher. Unfortunately, summing theoutput of a large number of transistors via a transformer is problematicbecause the transformer can cause dangerous overvoltage in thetransistors.

SUMMARY OF THE INVENTION

The present invention solves these and other problems by providing asolid-state high-voltage pulse generator based on a three-phase choppercapacitance charger. In the first phase, an intermediate capacitor isresonance-charged via a diode. In the second phase, the intermediatecapacitor is discharged to the load through one or more solid-stateswitches. In the third phase, the energy remaining in the intermediatecapacitor is returned to the power-supply filter capacitor.

In one embodiment, the three-phase chopper includes an intermediatecapacitor that is charged by first and fourth branches of a bridge anddischarged by second and third branches of a bridge. In one embodiment,each branch of the bridge includes a diode in series with an inductor.In one embodiment, a composite solid-state switch connects theintermediate capacitor to a primary winding of an output transformersuch that the intermediate capacitor discharges through the primarywinding. In one embodiment, a secondary winding of the outputtransformer is provided to an output load. In one embodiment, the outputload is a reactive load. In one embodiment, the output load is acapacitive load.

In one embodiment, an output transformer is used at the output of thethree-phase chopper. In one embodiment, a separate three-phase chopperis used to drive each primary winding of an output transformer havingmultiple primary windings. In one embodiment, the output transformerincludes a split magnetic core transformer. In one embodiment, theoutput transformer includes a Tesla transformer. In one embodiment, theferrite rod is made of toroidal magnetic ferrite cores.

In one embodiment, a second stage compressor is used. In one embodiment,the second stage compressor includes a blumline.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features of the disclosed invention will readily beappreciated by persons skilled in the art from the following detaileddescription when read in conjunction with the drawings listed below.

FIG. 1 shows a prior art chopper based on a resonant charging circuit.

FIG. 2 shows voltage at the capacitor versus a quality factor of thetank circuit load for the chopper of FIG. 1.

FIG. 3 shows a prior art chopper based on a resonant charging circuitwith an anti-parallel diode.

FIG. 4 shows voltage at the capacitor versus a quality factor of thetank circuit load for the chopper of FIG. 3.

FIG. 5A shows a three-phase chopper.

FIG. 5B shows a three-phase chopper using Insulated Gate BipolarTransistors.

FIG. 6 shows voltage at the capacitor versus a quality factor of thetank circuit load for the chopper of FIGS. 5A-B.

FIG. 7 shows voltage at the switch for the three-phase chopper,including recovery of the voltage at the switch.

FIG. 8 shows a circuit for calculating transmission versus coupling forthe capacitance charger.

FIG. 9 shows energy transmission between the capacitance C1 and thecapacitance C2 versus coupling for the capacitance charger.

FIG. 10 shows coupling between primary and secondary windings of theTesla transformer versus the height of the ferrite column.

FIG. 11 shows a Tesla transformer for use with the capacitance charger.

FIG. 12 shows a cross section view of a split-core transformer for usewith the capacitance charger.

FIG. 13 shows a side view of the split-core transformer for use with thecapacitance charger.

FIG. 14 shows one embodiment of a capacitance charger with a split-coretransformer having four primary windings and a blumline compressor.

FIG. 15 shows a response of the blumline charged with a microsecondcapacitance charger.

FIG. 16 shows an output of the capacitance charger of FIG. 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a simple resonance charging system 100, where a powersupply 101 provides a DC output voltage through a diode 102. The powersupply 101 includes a filter capacitor 121 to filter the output voltageof the power supply 101. An output of the diode 102 is provided throughan inductor 103 to a first terminal of an intermediate capacitor C1 104.A second terminal of the capacitor C1 104 is provided to ground througha series connection of an inductor 105 and a primary winding 106 of atransformer 120. A solid-state switch 110 is provided between the firstterminal of the intermediate capacitor C1 104 and ground. A controlcircuit 111 controls the solid-state switch 110. A secondary 107 of thetransformer 120 is provided to a load 108. The charging system 100doubles the voltage of the filter capacitor 121 by charging theintermediate capacitor.

In one embodiment, the capacitor C1 104 is resonance charged to 320volts from a 160 volt DC power supply. When the solid-state switch 110is switched on, the capacitor 104 transmits the stored energy to theload 108 via the transformer 120. The transformer 120 multiplies thevoltage to a desired level. When the load 108 is resistive, the chargingsystem 100 is stable. When the load 108 is not resistive, as in the caseof a plasma application, the system 100 is extremely unstable. Consider,for example, how the charging voltage of the capacitor C1 104 depends onthe quality (Q-factor) of the load 108. The Q-factor of the load isgiven by Q-factor=R/sqrt(L_(stray)/C1), where sqrt( ) denotes the squareroot, and L_(stray) is a stray inductance of the transformer 120.

FIG. 2 is a plot showing the voltage at the capacitor 104 as a functionof the Q-factor of the load 108. FIG. 2 shows that the voltage on thecapacitor 104 depends on the Q-factor of the load (almost doubling asthe Q-factor deviates from unity). This means that the values of thevoltage of the capacitor and the switch must be chosen higher thanneeded in order to withstand the overvoltage when working with a loadhaving a high or low Q-factor.

FIG. 3 shows the circuit of FIG. 1 with the addition of a reverse-biasedanti-parallel diode 330 connected between the first terminal of thecapacitor 104 and ground. In power supply practice, such ananti-parallel diode is used to return the excess energy to the filtercapacitor 121.

FIG. 4 is similar to FIG. 2 and shows the voltage at the capacitor 104as a function of the Q-factor of the load 108 when the diode 330 isused. In FIG. 2, the voltage approximately doubles as the Q-factorvaries from 1 to 10. In FIG. 4, the voltage increases by only 32%(330v/250v) as the Q-factor varies from 1 to 10. Thus the diode 330improves performance in some respects. Nevertheless, the voltage variesexcessively with variations in the Q-factor of the load.

Further problems are related to the need for snubbers in the charger100. The rise time of the voltage at the switch 110 is short even for anIGBT or a MOSFET. A snubber circuit is typically used to eliminate falseswitching of the switch 110. It is known that the snubber circuitsconsume power, generate heat, and need more space. Moreover, it isdifficult to design a snubber circuit when MOSFET or IGBT transistorsare working in hard parallel.

The above problems are solved herein by using a three-phase chopper. Inthe first phase, an intermediate capacitor is resonance charged viafirst and second legs of a full-wave bridge. In the second phase, theintermediate capacitor is discharged to the transformer primary throughsolid state switches. In the third phase, the remaining energy in theintermediate capacitor returns to the power supply filter capacitorthrough third and fourth legs of the full-wave bridge.

FIG. 5A shows a three-phase chopper circuit 500 that avoids many of theproblems identified in the circuits of FIGS. 1 and 3. The chopper 500includes a bridge using four diode-inductor arms. An inductor L1 501provides current from a positive supply rail to an anode of a diode D1511. An inductor L2 502 provides current from a positive supply rail toa cathode of a diode D2 512. An inductor L3 503 provides current from anegative supply rail to an anode of a diode 513. An inductor L4 504provides current from the negative supply rail to a cathode of a diode514. The cathodes of diodes 511, 513 are provided to a first terminal ofan intermediate capacitor 550 and to a first terminal of a primarywinding 542 of a transformer 560. A second terminal of the primarywinding 542 is provided to a first terminal of a solid-state switch 530.A second terminal of the solid-state switch 530 is provided to theanodes of the diodes 512, 514, and to a second terminal of the capacitor550. A control output of a controller 111 is provided to a control inputof the solid-state switch 530. A secondary winding 541 of thetransformer 560 is provided to a load 108. The solid-state switch 530can be based on solid-state switch devices including MOSFETs, IGBTs,bipolar transistors, thyristors, etc.

The topology of the three-phase chopper 500 is that of a full-wavebridge having four branches and two diagonals. One branch corresponds tothe series combination of the inductor L1 501 and the diode L1 511. Onebranch corresponds to the series combination of the inductor L2 502 andthe diode L2 512. One branch corresponds to the series combination ofthe inductor L3 503 and the diode L3 513. One branch corresponds to theseries combination of the inductor L4 504 and the diode L4 514. Thepower supply 101 is provided in one of the diagonals. The capacitor C1550 is provided in the other diagonal.

FIG. 5B shows a three-phase chopper circuit 580 that is a specificembodiment of the three-phase chopper 500. In the three-phase chopper580, the switch 530 uses IGBTs. The chopper 580 includes the bridgeusing four diode-inductor arms. The inductor L1 501 provides currentfrom a positive supply rail to the anode of the diode D1 511. Theinductor L2 502 provides current from the positive supply rail to thecathode of the diode D2 512. The inductor L3 503 provides current fromthe negative supply rail to the anode of the diode 513. The inductor L4504 provides current from the negative supply rail to the cathode of thediode 514. The cathodes of diodes 511, 513 are provided to the firstterminal of the intermediate capacitor 550 and through the inductor 540to the first terminal of the primary winding 542 of the transformer 560.The second terminal of the primary winding 542 is provided to anodes offour diodes 521-524. Cathodes of the diodes 521-524 are provided,respectively, to the first terminal of the solid-state switches S1-S4531-534. The second terminals of the solid-state switches 531-534 areprovided to the anodes of the diodes 512, 514, and to the secondterminal of the capacitor 550. The control output of the controller 111is provided to control inputs of the parallel solid-state switches531-534. The secondary winding 541 of the transformer 560 is provided tothe load 108. The parallel solid-state switches 531-534 can besolid-state switch devices including MOSFETs, IGBTs, bipolartransistors, thyristors, etc.

In the first phase, the three-phase chopper 500, provides resonantcharging of the capacitor C1 550 through the diodes D1 511, D4 503 andthrough the inductors L1 501, L4 503. The resonant chargingapproximately doubles the voltage of power supply 2Vpc. The second phaseincludes discharging the capacitor 550 to the load 108 via thetransformer. If the discharge has good damping (e.g., the negative cycleof the sine wave is less than half of the positive cycle), then thediodes D2 512 and D3 513 do not conduct and the third phase is not used.If the discharge does not have a good damping (e.g., the negative sinecycle is more than half of the positive cycle), the diodes D2 512 and D3513 conduct and return the energy to the power supply (phase 3). Whenthis third phase is over the first phase starts again.

FIG. 6, like FIGS. 2 and 4, shows the capacitor voltage versus Q-factorof the load for the three-phase choppers 500, 580. FIG. 6 shows that themiddle of the curve (where Q is roughly equal to 1) is about 20% higherthan the ends of the curve (where Q is roughly equal to 0.1 and 10). Thevoltage reaches maximum when the circuit works at maximum power. Whenthe power decreases because of poor load matching, the voltage of thecapacitor and the switch decreases somewhat. When the load 108 hasreactive components, it reduces the voltage at the capacitor and theswitch instead of increasing it, thus providing good safe-operatingmargins.

FIG. 7 shows one example of the voltage across the four parallelsolid-state switches 531-534 together with the four diodes 521-524. FIG.7 shows that the voltage across the switch/diode combinations drops veryquickly from 170V to zero. In one embodiment, the conduction time isabout 3 us. After the conduction time is over, a negative voltageappears at the anode and restores the voltage to 150V at a speed ofapproximately 75V/us. The three-phase chopper 500 provides goodperformance without the need for snubbers.

In one embodiment, the switches 531-534 are IGBTs configured to work asthyristors, wherein the conduction time for the driver is approximately30% more than the current pulse. The diodes 521-524 stop the currentwhen it changes polarity. The inductor 540, typically a ferrite corewith one winding, reduces any overvoltage that occurs when the diodes521-524 turn off.

In one embodiment, the load 108 includes a high voltage capacitor thatis charged from the capacitor 550 via the transformer 560. Thetransformer steps up the voltage to a desired voltage. In oneembodiment, a relatively high reactive power is provided at the outputof the charger. In one embodiment, the transformer 560 includes a Teslatransformer. In one embodiment, the transformer 560 includes asplit-core transformer.

The efficiency of the system is dependent on the coupling coefficient ofthe transformer 560. FIG. 8 shows a circuit for calculating transmissionversus coupling for the capacitance charger 500. In FIG. 8, the primarycapacitance is C1 550 and the secondary capacitance is a capacitor C2805. The circuit of FIG. 8 is similar to the circuit of FIG. 1, exceptthat in FIG. 8, the load 108 has been replaced by the capacitor C2 805.

FIG. 9 shows energy transmission between the capacitance C1 550 and C2805 versus coupling of the transformer 120. FIG. 9 shows that anefficiency of more than approximately 80% corresponds to couplingbetween the windings of approximately 0.9 or more.

A typical Tesla high voltage transformer has a coupling coefficientbetween 0.5-0.6. However, when a ferrite is inserted in the innerwinding of the Tesla transformer, the coupling can be substantiallyimproved. The coupling coefficient of such transformer is shown in FIG.10 and the transformer is shown in FIG. 11. The transformer of FIG. 11includes one or more ferrite cores 1102 and an insulating (e.g.,plastic, lexan, etc.) tube 1104. A partial insulation 1106 between thecores prevents electrical breakdown between the high voltage winding andthe ferrite cores. A primary winding is placed on the outer diameter ofthe insulating tube 1104. The insulating tube 1104 provides insulation,especially when the electrical field is relatively undisturbed.

FIG. 10 shows example measured data of the transformer shown in FIG. 11when the height of the primary and secondary windings is 6″, and themain insulation tube has an outside diameter OD=2.75″ and an insidediameter ID=2.5″. In one embodiment, twelve ferrite cores OD=2.4″,ID=1.4″ and T=2.5″ are the cores of the transformer. FIG. 10 shows thecoefficient of coupling between windings versus height of the column offerrite. The transformer provides only 0.58 coupling without theferrite. The transmission is less than 30% without ferrite. By changingthe height of the ferrite column to 6″ the coupling coefficientincreases to 0.94 and the transmission to 85%.

In one embodiment, the output transformer includes a split magnetic coretransformer 1200 as shown in FIGS. 12 and 13. The cores of thetransformer 1200 include one or more air gaps. The air gaps are providedbecause of the presence of unipolar pulses at the output of the chopperand a low duty factor. Without the air gaps the unipolar pulses maysaturate the transformer. The air gaps provide a long negative pulsebetween positive pulses. If the duty factor is high, the air gaps canproduce oscillation. In one embodiment, one air gap is replaced with twogaps of half the size. This allows the high voltage winding to be madeseparately and then insert it between two cores. In one embodiment, aresin fill is used.

FIG. 14 shows one embodiment of a capacitance charger 1400 with asplit-core transformer 1407 having four primary windings, one secondarywinding, and a secondary blumline compressor 1410. The charger 1400includes four choppers 1403-1406. Each chopper 1403-1406 corresponds tothe chopper 500 shown in FIG. 5. Each chopper 1403-1406 drives aseparate primary winding of the transformer 1407. In one embodiment,each primary winding of the transformer 1407 has three turns in fourparallel wires. In one embodiment, the secondary winding of thetransformer 1407 has 32 turns. The coupling coefficient of thetransformer is approximately 42.6. A power supply 1401 provides DC powerto the choppers 1403-1406. In one embodiment, the power supply 1401includes a rectifier bridge which rectifies standard 110 volt AC toproduce a DC output of approximately 160V. A control circuit 1402controls all of the choppers 1403-1406, providing them with a 3 us pulseof 16. The total energy stored in the intermediate capacitors 550 in thechoppers 1403-1406 is 190 mJ. In one embodiment, the efficiency of thetransmission of the energy to a 1000 pF high voltage capacitor 1430 is81%.

An example of the final pulse at the end of the blumline 1410 is shownat FIG. 15. At 100 Ohms, the amplitude is 11.5 kV (shown as a curve1503). The current is 95A and the rise time of the voltage is 13 ns. Thelength of the pulse is 42 ns. The repetition rate is 1 kHz. The wholesystem (the charger and the compressor) can operate at up to 5 kHz. Themeasurements made for the customer showed a high reliability of thewhole system.

FIG. 16 shows an example output voltage of the capacitance charger 1400at 1000 pf capacitance, where the output is 10 kV and the charging timeis 1.6 us.

Although the foregoing has been a description and illustration ofspecific embodiments of the invention, various modifications and changescan be made thereto by persons skilled in the art without departing fromthe scope and spirit of the invention. Accordingly, the invention islimited only by the claims that follow.

1. A solid-state high-voltage pulse generator comprising: a bridgehaving first, second, third, and fourth branches and first and seconddiagonals, each of said first, second, third, and fourth branchescomprising a diode, said first diagonal comprising a power supply havingan output filter capacitor; an intermediate capacitor provided acrosssaid second diagonal, said intermediate capacitor charged by said powersupply through said first and third branches, said intermediatecapacitor discharged to said filter capacitor by said second and fourthbranches; an output transformer having at least one primary winding andat least one secondary winding; a series circuit comprising asolid-state switch in series with said primary winding, said seriescircuit provided in parallel with said intermediate capacitor; and acontrol circuit to control said solid-state switch.
 2. The solid-statehigh-voltage pulse generator of claim 1, wherein each of said first,second, third and fourth branches comprises a diode in series with aninductor.
 3. A solid-state high-voltage pulse generator comprising: abridge having four branches wherein each branch comprises a diode; apower supply having an output filter capacitor, said power supplyprovided to a first diagonal of said bridge; a first capacitor providedto a second diagonal of said branch, said first capacitor charged bycurrent through first and fourth branches of said bridge and dischargedby current through second and third branches of said bridge; asolid-state switch configured to provide said capacitor to a primarywinding of an output transformer; and a control circuit to control saidsolid-state switch.
 4. The solid-state high-voltage pulse generator ofclaim 3, wherein said solid-state switch comprises a plurality ofsolid-state devices provided in parallel.
 5. The solid-statehigh-voltage pulse generator of claim 3, wherein each branch of saidbridge comprises a diode in series with an inductor.
 6. The solid-statehigh-voltage pulse generator of claim 3, wherein said output transformercomprises multiple primary windings.
 7. The solid-state high-voltagepulse generator of claim 3, wherein a secondary winding of said outputtransformer is provided to a capacitor.
 8. The solid-state high-voltagepulse generator of claim 3, wherein a pulse shape of a pulse provide bya secondary winding of said output transformer is compressed by acompressor circuit.
 9. The solid-state high-voltage pulse generator ofclaim 3, wherein said output transformer comprises a split-coretransformer.
 10. The solid-state high-voltage pulse generator of claim3, wherein said output transformer comprises a Tesla transformer. 11.The solid-state high-voltage pulse generator of claim 10, wherein saidoutput transformer comprises a Tesla transformer with at least a partialferrite core.
 12. A method for producing a high-voltage pulse,comprising: resonance charging a capacitor using current provided by apower supply through first and second legs of a reactive bridge; closinga solid-state switch to connect a primary winding of an outputtransformer between said first and second legs; discharging saidcapacitor to said primary winding; and returning charge remaining insaid capacitor to said power-supply through third and fourth legs ofsaid bridge.
 13. The method of claim 12, wherein said solid-state switchcomprises a plurality of solid-state devices in parallel.
 14. The methodof claim 12, wherein each branch of said bridge comprises a diode inseries with an inductor.
 15. The method of claim 12, wherein said outputtransformer comprises multiple primary windings.
 16. The method of claim12, further comprising providing an output pulse from said outputtransformer to a capacitor.
 17. The method of claim 12, furthercomprising compressing an output pulse of said output transformer. 18.The method of claim 12, wherein said output transformer comprises asplit-core transformer.
 19. The method of claim 12, wherein said outputtransformer comprises a Tesla transformer.
 20. The method of claim 12,wherein said output transformer comprises a Tesla transformer with atleast a partial ferrite core.
 21. An apparatus for producing ahigh-voltage pulse, comprising: a full-wave reactive bridge comprisingfirst, second, third, and fourth legs; means for resonance charging acapacitor using current through said first and second legs; means forpartially discharging said capacitor to a primary winding of an outputtransformer; and means for further discharging said capacitor throughsaid third and fourth legs.
 22. The apparatus of claim 21, furthercomprising means for compressing an output pulse of said outputtransformer.
 23. A solid-state high-voltage pulse generator comprising:a full-wave bridge having first, second, third, and fourth branches,wherein each of said first, second, third, and fourth branches comprisesa diode in series with a reactive element; a direct current power supplyprovided to said full-wave bridge; a first capacitor provided betweensaid first and fourth branches such that said capacitor is charged bycurrent through said first and fourth branches and discharged by currentthrough said second and third branches; a solid-state switch configuredto connect a primary winding of an output transformer in parallel withsaid capacitor such that said capacitor discharges through said primarywinding; and a control circuit to control said solid-state switch. 24.The solid-state high-voltage pulse generator of claim 23, wherein saidsolid-state switch comprises a plurality of solid-state devices inparallel.
 25. The solid-state high-voltage pulse generator of claim 24,wherein each branch of said bridge comprises a diode in series with aninductor.
 26. The solid-state high-voltage pulse generator of claim 24,wherein said solid-state switch comprises one or more Insulated GateBipolar Transistors.
 27. The solid-state high-voltage pulse generator ofclaim 24, wherein said solid-state switch comprises one or more MOSFETS.28. The solid-state high-voltage pulse generator of claim 24, whereinsaid solid-state switch comprises one or more thyristors.